Control of loudness, sound quality and vocal efficiency in speech and voice production are not well understood. Effective communication sometimes depends upon maximizing vocal intensity and vocal endurance, especially in certain professions and avocations. The long range goal of this proposal is to study vocal efficiency and optimal control of the voice through empirical and theoretical studies based on trained and untrained vocalists. The specific goals of this proposal are to 1) develop a quantitative theory of loudness control based on physiologic and acoustic variables, 2) study and explain the mechanisms of loudness control in trained vocal performers, 3) explore concepts of efficiency in phonation, 4) interpret modes of phonation on the basis of glottographic, airflow and acoustic signals, and 5) study acoustic,, aerodynamic and glottographic correlates of vocal fatigue. The scientific gains should contribute significantly to clinical and studio diagnostic and intervention concepts and techniques.